Duncan spent 39 years in the Royal Navy, retiring as Vice Admiral in 2018. Since then, he has built a portfolio career in Defence and Security consultancy and the charitable sector. He has been a lifelong fly fisherman, having got his first fly rod for his 8th birthday. He has been a member of the Portsmouth Services Fly Fishing Association since the mid 1980s and its Chairman since 2009. Throughout this time he has fished the Itchen and Meon. For the Test and Itchen Association, he advises on the Meon and helps the Executive Director with strategy.